When a driver presses on a gas pedal in a vehicle, torque is requested from an engine through a driveline. If the driveline had previously been communicating little or no torque to a set of wheels, as when the vehicle is at rest or coasting, the driveline will be slack. This slack, or lash, is taken up rapidly when torque is applied, resulting in a collision between driveline gears and a clunk noise. The compliance of the driveline allows oscillatory behavior after the clunk, which stresses driveline components. Even when the driveline is providing positive torque, a rapid change in torque may excite the oscillatory behavior. Various methods have been employed to combat this problem of clunk and oscillation.
Referring now to FIG. 1, a block diagram of a clunk management system according to the prior art for an engine without electronic throttle control (ETC) is depicted. A pedal 102 controls an engine throttle body 104 within an engine 106. A position of the pedal 102 is communicated to a torque comparator 108 and a spark advance calculator 110. Engine sensors 112 (e.g., RPM, etc.) provide data to the torque comparator 108 and to the spark advance calculator 110. The spark advance calculator 110 provides a spark advance signal to ignition coils 114. The ignition coils 114 cause spark plugs (not shown) to fire at the specified times.
The torque comparator 108 compares the current torque being produced by the engine 106 with the requested torque according to the pedal 102. If the requested torque would cause the driveline to clunk or oscillate, the torque comparator 108 instructs the spark advance calculator 110 to increase spark retard. This deviation from optimal engine operation reduces the output torque while lash is being taken up.
Referring now to FIG. 2, a block diagram of a clunk management system according to the prior art for an engine with electronic throttle control (ETC) is presented. A pedal 120 inputs pedal position to an electronic throttle control system 122. The electronic throttle control system 122 provides a requested throttle position to a blade rate limiter 124, a torque comparator 126, and a spark advance calculator 128. Engine sensors 130 (e.g., RPM, etc.) within an engine 132 provide information to the torque comparator 126 and to the spark advance calculator 128.
The spark advance calculator 128 calculates an appropriate spark advance and communicates it to ignition coils 132. The torque comparator 126 compares the current engine torque with the requested torque from the electronic throttle control 122. If the requested torque will cause driveline clunk or oscillation, the torque comparator 126 instructs the blade rate limiter 124 to slow the opening of an engine throttle 134. In this way, the output torque of the engine 132 is reduced while driveline lash is taken up.